Ok, lets say they did release the source code, and just for the moment lets assume it would be the current version of the game (zone files and all that).
What's the real point? So someone can setup their own server that, at most, maybe a couple people might log into a few times and then go back to the real Arctic where there are actually people?
The truth is that people just won't play a fake Arctic. They want the real thing with all of the chaos and drama. Also, we have low enough numbers as it is that attempting to divide the player base will only result in an even quicker decline than might already be happening (course, people have been crying about the death of the game for the past 5+ years and it's yet to happen).
The only real result in releasing the code would probably be a lot more abuse because you know at least a few people will dig through the code just to figure out how to manipulate the game mechanics to their advantage. It would end up creating even more work for the Imm staff just to fix possible bugs and odd game mechanics that might never otherwise have been discovered.
In a nutshell...
Releasing the code would be totally pointless since nothing would ever come of it (in terms of another mud actually being created from it that wouldn't crash and burn).